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General Packet Radio Service (GPRS)

General Packet Radio Service (GPRS). MS. BSS. MS. BSS. PACKET UPLINK ASSIGNMENT. PACKET UPLINK ASSIGNMENT. PACKET UPLINK ASSIGNMENT. PACCH. PAGCH. PAGCH. MAC: TBF Establishment. MS initiated One Phase Access, or Two Phase Access. PACKET CHANNEL REQUEST. PRACH.

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General Packet Radio Service (GPRS)

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  1. General Packet Radio Service(GPRS)

  2. MS BSS MS BSS PACKET UPLINK ASSIGNMENT PACKET UPLINK ASSIGNMENT PACKET UPLINK ASSIGNMENT PACCH PAGCH PAGCH MAC: TBF Establishment • MS initiated • One Phase Access, or • Two Phase Access PACKET CHANNEL REQUEST PRACH PACKET CHANNEL REQUEST PRACH PACKET RESOURCE REQUEST PACCH TBF Est. By MS: One Phase Access TBF Est. By MS: Two Phase Access

  3. MS BSS PACKET PAGING REQUEST PPCH PACKET CHANNEL REQUEST PRACH PACKET IMMEDIATE ASSIGNMENT PAGCH PACKET PAGING RESPONSE PACCH PACCH or PAGCH PACKET DOWNLINK ASSIGNMENT TBF Est. By Network MAC: TBF Establishment • Network initiated

  4. MAC: Channel Access & Resource Allocation • Slotted Aloha • Used in PRACH • MSs send packets in uplink direction at the beginning of a slot • Collision: Back off -> timer (arbitrary) -> re-transmit • Time Division Multiple Access (TDMA) • Predefined slots allocated by BSS • Contention-free channel access • All logical channels except PRACH

  5. QoS Support • End-to-end QoS may be specified by Service Level Agreements • Assumes that IP multimedia applications are able to • Define their requirements • Negotiate their capabilities • Identify and select available media components • GPRS specifies signaling that enable support for various traffic streams • Constant/variable bit rate • Connection oriented/connection less • Etc.

  6. QoS Profile for GPRS Bearers • Describes applications characteristics and QoS requirements • 4 parameters: • Service precedence • 3 classes • Reliability parameter • 3 classes • Delay parameters • 4 classes • Throughput parameter • Maximum and mean bit rates

  7. QoS Profile for GPRS Bearers • QoS profile is included in Packet Data Protocol (PDP) context • Negotiation managed through PDP procedures (activation, modification and deactivation)

  8. Packet Classification and Scheduling • TBF tagged with TFI • TFI different for each TBF • Packet scheduling algorithms are not defined by the standard; defined and implemented by GPRS network designers and carriers • GPRS *can* enable per-flow quantitative QoS services with proper packet classification and scheduling algorithms...Hmmm.

  9. Mobility Management • Two procedures: • GPRS Attach/Detach (towards SGSN/HLR) • Makes MS available for SMS over GPRS • Paging via SGSN • Notification of incoming packet • PDP Context Activation/Deactivation • Associate with a GGSN • Obtain PDP address (e.g. IP)

  10. GPRS Mobile “Station” States • GPRS protocol stack (MS) can take on 3 different states • IDLE • STANDBY • ACTIVE/READY • Data can only be transmitted in the ACTIVE state

  11. Routing to MS • IDLE state • No logical PDP context activated • No network address (IP) registered for the terminal • No routing of external data possible • Only multicast messages to all GPRS handsets available

  12. Routing to MS • STANDBY state • Only routing area is known • RA is defined by operator => allows individual optimizations • When downlink data is available, packet paging message is sent to routing area • Upon reception, MS sends it's cell location to the SGSN and enters the ACTIVE state

  13. Routing to MS • ACTIVE state • SGSN knows the cell of the MS • PDP contexts can be activated/deactivated • Can remain in this state even if not data is transmitted (controlled by timer)

  14. PDP Contexts • Packet Data Protocol (PDP) • Session • Logical tunnel between MS and GGSN • Anchored GGSN for session • PDP activities • Activation • Modification • Deactivation

  15. PDP Context Procedures • MS initiated MS BSS SGSN GGSN Activate PDP Context Request Create PDP Context Request Create PDP Context Response Activate PDP Context Accept

  16. PDP Context Procedures • GGSN initiated MS BSS SGSN GGSN Packets from ext. nw. PDU notification req. PDU notification resp. Request PDP Context activation Create PDP Context Request Activate PDP Context Request Create PDP Context Response Activate PDP Context Accept

  17. Secondary PDP Contexts • Used when the QoS requirements differ from Primary PDP Context • Same IP address • Same APN • E.g., for IMS; signaling on primary PDP context and user data on secondary PDP context

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